NO to focusing on the Rangers (remember TLOTR?)
NO to retelling the same story (the beauty of B5 was not knowing what was coming)
NO to Technomages (not relevant enough)
NO to continuing Crusade (boring story which is why it failed)
NO to original actors playing different roles (It wouldn't be right!)

YES to ignoring the book continuity and telling the universe after the end of original B5
This means:
Casting of original actors wouldn't matter because the series would be set in the future and age is no issue
Tell the stories that weren't ended on screen:
1) Telepath War and future of Psi Corps/Lyta's resistance
2) Centauri Prime under the Drakh (WWE was a possible future as was Babylon Squared - see Coming Of Shadows (the telepath escort) and Point Of No Return (Lady Morella))
3) Earth/Mars post Clark
4) Rebuilding of Narn
5) Mimbar after civil war

At least I can then get over watching Sleeping In Light and thinking - 'But what about this?...What about that?